1. Field
The presently disclosed subject matter relates to outer casings for headlights, and to headlights using the outer casings. More particularly, the disclosed subject matter relates to outer casings including a thin outer lens, which can be casted by a simple molding tool that can prevent an occurrence of burr(s) on the outer lens, and to headlights using the outer casings, which can incorporate various lamps such as a low beam headlight with a high airtight structure and an adequate mechanical strength even when the outer lens is formed in a thickness of less than 2.5 millimeters.
2. Description of the Related Art
Conventional general headlights frequently incorporate various lamps such as a low beam headlight, a high beam headlight, a turn signal lamp and the like into an outer casing, which is devised so as to match with a design of a vehicle as a front combination lamp. The outer casing is generally composed of a casing to fix the various lamps and an outer lens attached to the casing so that light emitted from the various lamps can be emitted in a light-emitting direction for each of the lamps.
The outer casing may also perform a sealing function to protect the various lamps from a fluid such as rain, a dust such as dirt on a road, etc. In addition, in accordance with a trend of automotive lighting and for purpose of an improvement of fuel efficiency, the outer casing has been constantly required to be reduced in weight, along with the various lamps incorporated therein, while maintaining an adequate mechanical strength.
Accordingly, the outer lens, which can be formed in a thin thickness, has been constantly required to cause a reduction in weight for headlights in addition to efficiently transmitting the lights emitted from the various lamps. Moreover, even when the outer lens can be formed in a thin thickness, the outer lens can be attached to the casing with confidence while the outer casing is maintained at a high air proof efficiency and an adequate mechanical strength.
FIG. 6 is a top view showing a conventional general outer lens for a headlight. The outer lens 80 is composed of a facing portion 88 and a sealing rib 86, and can be made by a molding injection method using a thermoplastic polycarbonate resin as a raw material. FIG. 7 is a side cross-sectional view showing the conventional outer lens 80 taken along line A-A shown in FIG. 6, in a case where the outer lens 80 is casted by a molding tool.
The molding tool includes: a cavity die 81; a core die 82 being mold-clamped to the cavity die 81; a first cavity 89 casting the facing portion 88; a second cavity 87 casting the sealing rib 86; an inlet 83 injecting a plasticized raw material; a cold runner 84 passing through the plasticized raw material; and a gate 85 filling the plasticized raw material in the second cavity 87 and the first cavity 89 in turn, as shown in FIG. 7. Thereby, the molding tool may cast the outer lens 80 as shown in FIG. 6.
In this case, a maximum injection pressure of 180 MPa is used to inject the plasticized raw material in the first and the second cavities 89 and 87 spaced between the cavity die 81 and the core die 82. Accordingly, a huge force may be applied to a parting line 90 located between the cavity die 81 and the core die 82 in a detaching direction of the cavity die 81 and the core die 82.
As a result, the plasticized raw material may invade into a thin space of the parting line 90, and therefore may cause a burr on the outer lens 80 casted by the first cavity 89 and the second cavity 87 during the molding process. In addition, when the core die 82 is detached from the cavity die 81, because the burr drops from the parting line 90 and then occasionally adheres to a product of the outer lens 80, it sometimes happens that the burr disfigures the product of the outer lens 80.
When the burr occurs on the product, the product including the burr needs to be provided with an additional process for removing the burr after the molding process. In this case, the additional process may cause declining productivity and an increase in production costs. Therefore, a molding tool in which a burr does not occur in the molding process is desired to cast a product even when a thickness of the product is thin.
FIG. 8 is a graph showing a relationship between a thickness of a general molding product and an injection pressure. As the thickness of the molding product becomes thin, a higher injection pressure is required to cast the molding product. When a polycarbonate plate of 500 mm2 is casted in thicknesses of 4 mm, 3 mm, 2 mm and 1 mm, an injection pressure of 50 MPa (in case of the thickness of 4 mm) to 180 MPa (in case of the thickness of 1 mm) may be required to cast the polycarbonate plate, because a viscosity of the polycarbonate resin is relatively high.
Accordingly, when the outer lens 80 having a thinner facing portion 88 is casted by a molding tool, because a much larger force may be applied to the parting line 90 located between the cavity die 81 and the core die 82 in a detaching direction of the cavity die 81 and the core die 82, the larger force may be associated with a high probability of an occurrence of the burr.
In the conventional general outer lens 80, when the outer lens 80 including the facing portion 88 having a thickness of 2.5 mm to 3.5 mm is casted by a molding tool, the burr may barely occur on the outer lens 80. However, when the outer lens 80 including the facing portion 88 having a thickness of less than 2.5 mm is casted by the molding tool, the burr may occasionally occur on the outer lens 80.
A conventional molding tool, in which a burr may hardly occur even when a thin molding product is casted, is disclosed in Patent Document No. 1 (Japanese Patent No. 3,112,717). FIG. 9 is a schematic side cross-sectional view of a basic structural concept of the conventional molding tool to cast a casing having a thin thickness, which is disclosed in Patent Document No. 1.
The conventional molding tool 70 includes: a cavity die 72 including a centering location structure 76; a core die 71 being mold-clamped to the cavity die 72; a slide die 74 being mold-clamped to the cavity die 72 and the core die 71; a cavity 77 casting a thin casing; an inlet 75 for injecting a plasticized raw material; and a gate 75a for filling the plasticized raw material in the cavity 77. Thus, the molding tool 70 may cast the thin casing corresponding to a shape of the cavity 77.
In this case, a parting line 73 may be located between the slide die 73 and both the cavity die 72 and the core die 71, and the slide die 74 may move in a direction of arrow 74a. An injection pressure may be applied in a direction of arrow 77a when the molding tool 70 injects the plasticized raw material into the cavity 77. Accordingly, a huge force for the injection pressure may be applied in the direction of arrow 77a, which is parallel to the direction of the parting line 73. Therefore, even when the casing having a thin thickness is casted by the molding tool 70, the conventional molding tool 70 may prevent an occurrence of the burr on the casing such that is caused by the parting line 73.
The above-referenced Patent Documents is listed below, and is hereby incorporated with its English abstract in its entirety.    1. Patent Document No. 1: Japanese Patent No. 3,112,717
However, the structure of the conventional molding tool 70 includes the slide die 74 having the parting line 73 moving in the direction of arrow 74a, in addition to the cavity die 72 including the centering location structure 76 and the core die 71, which move in a parallel direction with the parting line 73. Accordingly, because the conventional structure is complex, design and a manufacture of a molding tool based upon the conventional structure may require great care and time. Moreover, the structure may cause a reduction of productivity as compared with the conventional manufacturing method for the outer lens due to the complex structure.
The disclosed subject matter has been devised to consider the above and other problems, features, and characteristics. Thus, embodiments of the disclosed subject matter can include outer casings for headlights, in which an outer lens having a facing portion can be casted without (or with reduced numbers of) an occurrence of burr(s) by a simple molding tool in common with a conventional molding tool for an outer lens even when the facing portion is casted in a thin thickness. The disclosed subject matter can also include headlights using the outer casings, which can incorporate various lamps such as a low beam headlight, a position lamp and the like with a high airtight structure and an adequate mechanical strength even when the facing portion of the outer lens is formed in a thin thickness of less than 2.5 millimeters.